# Fitting a Surface By Least Squares in Microsoft® Excel

## Chapter 4, Printout 4

1. Enter the data.

• Type "x1" in cell A1; then, in cells A2-A18, enter the Air Flow data from Table 4.8 (p. 150).

• Type "x2" in cell B1; then, in cells B2-B18, enter the Cooling Water Inlet Temperature data from the table.

• Type "x3" in cell C1; then, in cells C2-C18, enter the Acid Concentration data from the table.

• Type "y" in cell D1; then, in cells D2-D18, enter the Stack Loss data from the table.

Screenshot:

2. Compute the multiple linear regression and display related plots.

• Select "Tools --> Data Analysis."

• In the dialog that follows, select "Regression" from the list of options.

Screenshot:

• Click "OK."

• Fill out the resulting dialog box as follows:

Input Type Label Value
Input Y Range: \$D\$1:\$D\$18
Input X Range: \$A\$1:\$C\$18
Labels checked
Constant is Zero unchecked
Confidence Level unchecked
New Worksheet Ply: selected
New Worksheet Ply:
Residuals checked
Residual Plots checked
Standardized Residuals checked
Line Fit Plots unchecked
Normal Probability Plots checked

Screenshot:

• Click "OK."

Excel creates a new sheet in the workbook with the summary statistics, plots of residuals vs. x1, x2, and x3, and a normal probability plot.

Screenshot (summary output):

Note: you can resize all columns to fit their contents by selecting all the cells you want to resize, then selecting "Format --> Column --> Autofit Selection."

Screenshot (plots):

Note: you can move the charts as necessary by clicking a blank area in the chart and dragging it to a new location. Other changes can be made by double-clicking various elements in the charts.